When Boeing designed the 747, the world’s first wide-body, twin-aisle airliner powered by high bypass ratio turbofans, in the 1960s, it deliberately placed the cockpit on a short upper deck so that it could be alternatively used as a freighter, with straight-in nose loading, after the supersonic era arrived. While that era did eventually dawn and there were three such supersonic aircraft that either entered scheduled service or were at least conceptualized, it was hardly the successful next-wave envisioned. What went wrong?
Aerospatiale-British Aerospace Concorde
The Aerospatiale-British Aerospace Concorde was the only truly successful supersonic design.
In 1954, Great Britain’s Royal Aircraft Establishment first met to discuss whether future commercial aircraft should fly at higher subsonic speeds than those of the 500-mph Comet or eclipse the subsonic line altogether. Initial research, however, indicated that a Mach 1-exceeding transport could only attain its needed transatlantic range with a 300,000-pound gross weight, a paltry 15-passenger payload, and a five-and-a-half-fold increase in operating costs over long-range subsonic aircraft.
The key to such supersonic performance was the delta wing with a sharp, well-swept leading edge. Dietrich Kuechemann, a former Messerschmitt designer, discovered that such a configuration would reduce air resistance and drag at supersonic speeds and produce a stabilizing vortex.
It was also discovered that aircraft transmit pressure to the surrounding air by means of molecular collision, and when their speeds approach those of sound, they are expressed as “Mach numbers,” or the ratio of the body’s actual speed to that of sound. When they are identical, equality is achieved and expressed as “Mach 1.” That speed, however, varies with temperature: at the standard sea-level temperature of 59 degrees Fahrenheit, for instance, it is approximately 761 mph, while at -70 degrees Fahrenheit, or at about 40,000 feet of altitude, it decreases to 660 mph.
When pressure disturbances occur ahead of an aircraft flying at subsonic speeds, the air is able to “yield”, or “get out of the way”, before the aircraft actually passes through it, but at supersonic speeds, it is unable to do so fast enough, thus “piling up” and creating shock waves which ultimately explode in a ground-only detectable, thunderclap-like sonic boom.
Integral, therefore, to a supersonic design is its highly swept, sharp leading-edge airfoil. The thinner the wing, the less is the airflow’s speed over it, resulting in a more favorable wing upper surface pressure gradient and a reduction in drag.
While Great Britain explored the supersonic realm and the then-named British Aircraft Corporation proposed a supersonic transport designed the BAC-223, France was also designing such an airliner based upon its Sud-Est (later Aerospatiale) Caravelle.
Because of the financial commitment needed to launch a program of this magnitude, and because the British and French designs offered many similarities, an agreement was ultimately concluded to jointly develop an Anglo-French supersonic transport based upon the BAC-223 and the Super Caravelle, reducing costs and creating a single, technologically superior airframe for an envisioned smaller than traditional market for this type of aircraft.
On November 29, 1962, the resultant Supersonic Aircraft Agreement, entailing joint design, development, and manufacture was signed.
The first Concorde prototype, designated aircraft 001, had an overall length of 184.6-feet and a 326,000-pound gross weight and was first rolled out in Toulouse, France, on December 11, 1967. The second prototype, 002 followed ten months later in Filton, UK.
Aircraft 001, the first to fly, took to the skies on March 2, 1969, attaining a 250-knot speed and 10,000-foot altitude before flaring onto the runway and deploying its parachute after a 42-minute sortie. The British-assembled prototype followed on April 9 of the following year, but the French aircraft was the first to attain supersonic velocity, reaching Mach 1.00 on October 1 and Mach 2.00 on November 4.
The first firm Concorde order, by BOAC for five aircraft, was officially announced by the British Aircraft Corporation on May 25, 1972, and the contract signed two months later, on July 28, the same date that Air France also ordered four of the type.
Appearing with a 203.9-foot overall length, the production aircraft, with an eight-foot, 7½-inch width and a 6.5-foot height, accommodated 144 four-abreast passengers at a 32-inch seat pitch in its narrow, 129-foot-long cabin. This could alternatively be reduced to 128 passengers at an increased 34-inch pitch.
Powered by four, 38,050 thrust-pound Rolls Royce/SNECMA Olympus 593 Mk 610 turbojets fitted with 17-percent afterburning thrust and Type 28 thrust reversers, it featured an 83.10-foot, ogival-shaped wing whose 3,856-square-foot area resulted in a 100-pound-per-square-foot loading.
The first production aircraft, registered F-WTSB, first flew from Toulouse on December 6, 1973, remaining airborne for two hours, 40 minutes, and attaining a maximum speed of Mach 1.57. A demonstration flight, conducted the following June, was supersonically flown round-trip from Boston to Paris, without landing, in less time than the one-way Paris-Boston subsonic sector operated by a Boeing 747 would have taken.
Although Air France took delivery of the first Concorde, a -205 series registered F-BVFA on December 19, 1975, and BOAC acquired its first, a series -203 registered G-BOAA on January 14, none of the other airlines that had placed purchase options for it, including Air Canada, Air France, Air-India, American, BOAC, Braniff, CAAC, Continental, Eastern, Iran Air, Japan Air Lines, Lufthansa, Middle East Airlines, Pan Am, Qantas, Sabena, TWA, and United, converted them to firm orders.
In the early 1970s, North Atlantic traffic stagnation, coupled with high-capacity Boeing 747 widebody equipment and rapidly rising fuel costs, wreaked economic havoc with most major airlines. Although the UK and France futilely tried to counteract this mindset by emphasizing that Concorde was intended for a different market that needed its speed to augment, and not drain, its business, none were convinced of this claim.
Because of the nature of supersonic operations, obstacles to it were many, including depletion of the ozone layer, excessive noise during takeoff and landing, and creation of the sonic boom in flight. But with only a dozen or so of these aircraft predicted to comprise the world fleet, their ratio of utilization was negligible to that of the military types, and their noise levels demonstrated on par with those of first-generation, Stage 1, four-engine jetliners.
Initially barred from entering transatlantic service to New York, the very route for which the Anglo-French supersonic had been designed, the type was dually inaugurated into scheduled, commercial service elsewhere instead. On January 21, 1976, BOAC departed London-Heathrow for Bahrain in the Middle East with aircraft G-BOAA and Air France took off from Paris at the same moment for Dakar in Africa and Rio de Janeiro in South America with aircraft F-BVFA.
During a subsequent noise evaluation flight test on October 19, 1977 by Air France Concorde F-WTSB to New York-JFK, a landing on Runway 4-Left produced a 105.5-decibel reading, while its takeoff failed to register any number between the preset 105- and 112-decibel range at all, clearing it for operation.
Once again subjected to a dual-carrier inaugural event on November 22, 1977, Air France and British Airways supersonically linked the European continent with the US for the first time, and the daily round-trip services to London and Paris subsequently sustained load factors in excess of 80 percent.
In addition to New York and Washington, three weekly British Airways-Singapore Airlines interchange services operated between Bahrain and Singapore, the latter an extension of the London sector, while Braniff International operated six weekly, subsonic flights between Washington-Dulles and Dallas/Ft. Worth using both Air France and British Airways aircraft.
Of the 20 Concordes ultimately produced, two were prototypes, two were pre-production examples, and 16 were full-production airframes, with a decade having elapsed between the first flight of the prototype on March 2, 1969, and the last production aircraft, a series -216, on April 20, 1979. By that summer, the type had amassed 7,600 individual scheduled airline flights, having carried 360,000 passengers, and having logged 26,000 airborne hours.
Aerospatiale and British Aerospace were not the only aircraft manufacturers that produced a supersonic transport. The former Soviet Union designed its own counterpart, the Tupolev Tu-144.
Powered by four 38,500 thrust-pound engines, the aircraft featured a 188.5-foot overall length, an 83.10-foot span of its delta wing, and a 330,000-pound gross weight. Although, as expected, it resembled Concorde in configuration, there were several differences between the two.
In planform, its double-delta wing featured an ogival or s-shaped leading edge and trailing edge elevons but was devoid of camber or twist with a flat bottom. Its NK-144 turbojets, grouped in barely separated pairs, were air-accessed through its six-foot rectangular inlets on the leading edge and stretched across more than 17 feet to its exhaust pipes at the trailing edge.
First flying from Moscow’s Zhukovsky Airfield after executing a 25-second acceleration roll, the prototype, number 68001, remained airborne for 28 minutes with its landing gear extended the entire time. Unpressurized, it internally carried flight test equipment.
Although no photographs were released at the time, it is believed that a second airframe, numbered 68002, was damaged during its own flights and a third, 68003, was used for static testing.
Fuel thirsty and range-deficient, the type, requiring 100-passenger load factors to even meet breakeven costs, indicated the need for extensive redesign, which resembled Concorde to an even greater degree.
Stretched, the fuselage, now with a 215.5-foot length and sporting 34 as opposed to the previous 25 windows, facilitated accommodation of up to 140, and its droop nose, of greater length, introduced side windows.
Two canards, installed on the upper fuselage immediately behind the cockpit, extended out and forward to improve the aircraft’s low-speed handling characteristics.
The compound swept, full delta wing, 94.5 feet in span, offered variable camber and sculpting and a circular underside.
The engines, with square inlets, were repositioned further outboard and there was a greater separation between their pairs, while the main undercarriage units, of shorter length, retracted into them.
Numbered 77101, the first prototype of this extensively redesigned version first flew in August of 1972, while the second, 77102, was the first exhibited in the West at the 1973 Paris Air Show. Its pride was short-lived, however.
During a demonstration flight on June 3, the aircraft made a low pass with its canard surfaces and undercarriage extended, before executing a steep, afterburner-augmented climb. Appearing to experience a stall at 3,000 feet, it commenced a dive, abruptly leveling off only a few feet above the ground, at which point the right-wing tore off at the root. Spitting flames from its engines, it rolled, and the other wing dislodged itself from the structure. Exploding and plummeting to the earth, it impacted, killing the six crew members on board, eight on the ground, and damaging more than a hundred buildings in Goussainville, France.
Although no official cause was ever found, the belief is that the Tu-144 attempted to land on the wrong runway, beginning a go-around when the error was discovered, placing it on a collision course with a Mirage fighter. Diving to avoid it, it was subjected to g-forces beyond the airframe’s capacity and too little altitude remained in which to recover.
After operating cargo and mail route proving flights between December of 1975 and 1976, the Tupolev Tu-144 entered scheduled service on the 2,400-mile segment between Moscow and Alma-Ata, Kazakhstan, on November 1 of the following year, operating 102 such services with an average of 70 passengers, before they were discontinued on June 6, 1978. The aircraft logged 181 airborne hours, of which 102 were at subsonic speeds.
Despite its extensive redesign, it failed to rectify its deficiencies. Still, excessively fuel-thirsty, it was only able to cover the 2,400-mile route with half of its payload capability, attained by deliberately leaving half of its seats unoccupied, and the cabin noise level, caused by the engines and the air conditioning required to counteract the external, skin friction created heat, was intolerable.
A succeeding Tu-144D, fitted with uprated, more economical Koliesov RD-36-51A turbines, while offering hope when it first flew on May 23, 1978, fared little better. A fire in the left engines, propagating to the fuselage, left insufficient power to reach an alternate airport, causing the aircraft to careen into a field and explode. Of the five crew members aboard, two were killed and three injured.
Although the type began route-proving flights on the 3,480-mile sector from Moscow to Khabarovsk on June 23 of the following year and it covered the distance in three hours, 21 minutes, it never proceeded to scheduled status. The noise, fuel consumption, and range parameters of supersonic flight could not be transcended for commercial operations, leaving the one prototype, the two pre-production aircraft, the nine production Tu-144s, and the five production Tu-144Ds as the only testaments to this fact.
United States aircraft manufacturers explored their own supersonic designs. Boeing, for example, considered a Mach 1.8 aircraft, accommodating 227 passengers. Lockheed’s concept was more ambitious and radical. It produced a design proposal incorporating an airfoil-shaped fuselage and a doubly compounded delta wing projected to achieve Mach 3 speeds. Capacity, however, was not unlike that of Boeing’s aircraft at 218. Designated NAC-60, North American’s concept closely resembled the military B-70 Valkyrie, itself a supersonic design with canards, a compound-swept delta wing, and four aft-mounted engines grouped in pairs. It was also slated for the Mach 3 speed realm.
Boeing’s 2707-100, numerically considered the first of the second supersonic generation of airliners after its 707, was ultimately selected on December 31, 1966. Unlike the UK and USSR aircraft, it was intended, from the outset, to eclipse the boundaries of traditional configuration, structure, and speed, offering an extended service life.
Featuring titanium construction to withstand the 500-degree Fahrenheit structural temperatures generated by the friction of its intended, 1,800-mph/Mach 3 cruise speed, it sported a variable geometry delta wing, which pivoted on screw jacks and titanium bearings to cater to the extreme velocity variations, ranging from low subsonic approach speeds in the extended position to high supersonic cruise ones in the retracted one. Trailing edge flaps were fitted for the former portion of flight.
Power was to have been provided by four General Electric, wing-underside attached engines.
A full-scale wooden mockup of the supersonic airliner, intended to carry 300 passengers, was built.
Although the 113 optioned orders placed by 26 worldwide airlines seemed promising in June of 1967, the ambitious design exceeded the technological expertise required to transform it into reality. Aside from the inherent instability, it demonstrated during wind tunnel tests, the weight of the swing-wing aircraft was prohibitively excessive, carrying a 40,000-pound penalty and leaving less available for the fuel needed to provide the range that carriers sought.
Yet, because the type, as envisioned in its initial version, failed to offer acceptable payload and range capabilities, a second, the 2707-200, was proposed. Although it featured an elongated fuselage and Tu-144-resembling canards above and behind the cockpit, it weighed in at 750,000 pounds, which was 25 percent higher than envisioned and greater than that of a 500-passenger 747-100, and therefore failed to meet the FAA’s finalized design submission deadline.
Forced to abandon this variable-geometry airfoil concept, it produced a third version, the 2707-300. Featuring a 268.8-foot overall length, it incorporated the fixed, supersonic standard delta wing planform utilized by Concorde and the Tu-144, with a 141.8-foot span and an 8,497-square-foot area. The horizontal and vertical tailplane, with a 50.1-foot height, remained conventional.
Powered by four 60,000 thrust-pound General Electric GE4/J5P turbojets, it offered double the capacity and one-third more speed than its UK and USSR competitors, however, and was intended to transport 234 passengers 5,000 miles at 1,890-mph speeds at 60,000-foot service ceilings. The prototype’s 640,000-pound gross weight was expected to increase to 710,000 pounds on production aircraft.
In October of 1968, or five months before Concorde first flew, the definitive 2707-300 was chosen as the US’s supersonic transport design and construction of its prototype commenced in September of the following year, provisioning it as the third airliner in its class to enter the market. But it never would.
The obstacles characteristic of early 1960s commercial supersonic technology were numerous and insurmountable, including escalating research and production costs, increasing gross weights, decreasing ranges and payloads, rising seat-mile costs, excessive fuel burns and engine noise, the need for higher than subsonic fares, and the fear that first-class passengers would switch to the higher-speed transport, leaving the conventional, subsonic ones without the yield on which they depended for profitability.
Public, government, and aircraft manufacturer doubts concerning the 2707-300’s ability to ever economically achieve its projected noise, payload, and range design goals caused declining confidence, and on March 18, 1971, the House voted against it. Fifteen percent of the first 2707-300 airframe had been cut at the time, but, along with the wooden mockup, constituted the only evidence of the United States’ attempt to enter this market.
End of the Supersonic Era
Despite some two-and-a-half decades of sterling service, Concorde, the only supersonic airliner ever to achieve this status on a consistent basis, was brought back down to earth from a paltry height after a flight that lasted less than two minutes by a single piece of debris.
Transcending its V1 speed on Charles de Gaulle International Airport’s Runway 26R on July 25, 2000, aircraft F-BTSC, operating as Air France Flight AF 4590 to New York, treaded flames from its port wing underside, nosing down and plunging into a hotel in Genosse. All 109 crew members and passengers on board, as well as four on the ground, perished.
Grounded itself until November of 2001, the aircraft was subjected to scrutinized investigation, during which it was determined that a titanium alloy strip had been dislodged from the Continental Airlines DC-10-30 that had departed prior to it, rupturing one of the left tires. Disintegrating, it unleashed a barrage of pressure waves inside the number five fuel tank, which itself was just forward of the strike. The resultant release and gush of fuel ignited.
Several modifications were made after the accident investigation was completed. Installation of Kevlar linings to parts of fuel tanks one, four, six, and seven, and entirely to five and eight, for instance, were intended to reduce fuel flow in the event of similar ruptures to 0.5 liters-per-second as opposed to the estimated 100 liters-per-second sustained by the downed airliner. Tests were conducted with aircraft F-BVFB in France and G-BOAF in the UK.
Because a spark in the electrical bay was a possible cause of the first ignition, additional wire protection was installed. Michelin Near Zero Growth, or NZG, tires were also fitted to all eight main wheels. Finally, electrical power to the brake cooling fans was procedurally tuned off during takeoffs and landings.
Although these changes resulted in slightly higher weights and the Kevlar fuel tank linings reduced fuel capacity and range, the 20-kilo lighter tires partially counterbalanced these conditions.
Use of these changes was not long, however. Cost-prohibitive airframe life extension modifications to the five Air France and seven British Airways Concordes in service, along with increasing maintenance and fuel costs and declining traffic, all resulted in the decision to discontinue operations in 2003. Air France operated its last New York-Paris service on May 31 and British Airways followed suit on the New York-London route on October 31, ending a 27-year era of supersonic travel.
Supersonic Era Retrospect
The quest for speed to further shrink the world that airliners such as the de Havilland Comet and the Boeing 707 had already done at the dawn of the subsonic jet age was hardly what hindered the supersonic era. The lack of technical advancement to do so at a profit-generating cost, along with the inability to eliminate sonic boom noise and therefore remove its oceanic operational restrictions, was. While Boeing’s 2707 never proceeded beyond the mockup stage, the Tupolev Tu-144 only operated limited cargo service, and the Aerospatiale-British Aerospace Concorde was a technological success, it was not a commercial one. The speed-operating cost equation had thus not been satisfactorily solved.